The invention is based on methods and devices for determining the reset time and/or for drift compensation in a combustion chamber pressure sensor.
A combustion chamber pressure sensor in an internal combustion engine measures the pressure curve in the combustion chamber during operation of the engine. Usually, the piezoelectric or piezoresistive measurement principle is used for the measurement.
During operation, thermal influences generate stresses in the sensor that become apparent in the form of drift. The electronic evaluation of a piezoelectric sensor element is also very susceptible to drift due to leakage currents and insulation resistances. These drifts must be compensated for, either through continuous measurement and adjustment or through time-discrete resetting at a time in which an interference in the measurement signal is irrelevant. In the pressure curve evaluation currently in use, only the high-pressure phase is used (0-360° KW). The resetting time is only permitted to occur after this (360-720° KW); the intake pressure range of (540-720° KW) would be ideal. This ideal resetting time can only be determined in a very imprecise fashion because the combustion chamber pressure sensor does not receive a rotation angle position from the engine control unit and because engine speed and the pressure curve fluctuate sharply during operation.
DE 197 49 814 A1 has disclosed the execution of a correction in conjunction with a reference point in order to eliminate the zero error (drift) of the cylinder pressure sensor or cylinder pressure sensors. The reference point in this case can be a crankshaft angle at which the pressure is approximately known. This is the case, for example, at the TDC charge exchange (TDC=top dead center). In normally aspirated engines, the combustion chamber pressure or cylinder pressure at the TDC charge exchange is approximately equal to the ambient pressure.